Xerographic apparatus for applying ferromagnetic powder



March 19, 1963 F. H FRANTZ EIAL 3,081,737

XEROGRAPHIC APPARATUS FOR APPLYING FERROMAGNETIC POWDER Filed March 1, 1961 3 Sheets-Sheet l RVVENTURS FREDERICK H FRANTZ CARLA-ACKER AN ATTORNEYS March 19, 1963 F. H FRANTZ EIAL 3,081,737

XEROGRAPHIC APPARATUS FOR APPLYING FERROMAGNETIC POWDER Filed March 1, 1961 5 Sheets-Sheet 2 HVVENTURS FREDERICK H FRAN TZ BY CARLA ACKERMAN 7P '7 ATTORNEYS March 19, 1963 F. H FRANTZ El'AL 3,081,737

XEROGRAPHIC APPARATUS FOR APPLYING FERROMAGNETIC POWDER 5 Sheets-Sheet 3 Filed March 1, 1961 INVENTORS FR EDERICK H. FRANTZ CARL A. Ac ERMAN fl fya BY WW ATTORNEYS United States Patent Ofitice 3,081,737 Patented Mar. 19, 1963 3,031,737 XEROGRAPHIC APPARATUS FOR APPLYING FERROMAGNETIC POWDER Frederick H. Frantz, Vestal, N.Y., and Carl A. Ackerman, Brackney, Pa., assignors to General Aniiine & Film Corporation, New York, N.Y., a corporation of Delaware Filed Mar. 1, 1961, Ser. No. 92,543 6 Claims. (Cl. 118-637) This invention relates to the art of electrophotography and, more particularly, to the development of the latent image caried on an electrostatically charged sheet. Specifically, the invention pertains to improvements in the apparatus for applying developing powder to such sheets.

Electrophotography, also termed xerography, as exemplified in the patent to Carlson, USP 2, 297,691, is well known in the art, and various modifications have been made in apparatus utilizing this process. In one form, the paper itself has a coating of a photoconductive material which, after an electrostatic charge, may be exposed to light in contact with any original whereby a latent electrostatic image is produced. This image may be developed by applying a powder which adheres to the electrostatically charged portions representing the image. The developing powder is generally of a ferromagnetic material containing a coloring or toner substance for rendering the image visible. A thermoplastic substance may also be incorporated so that the toner may be fused to the base by heat in order to produce a permanent image.

Various types of devices have been developed in connection with electrophotographic apparatus for applying the developing powder to the charged and exposed sheet. In general, difficulty has been experienced in these devices with the uniformity of application of the ferromagnetic powder over the area of the sheet to be covcred, and also with the even distribution of the toner and carrier material. It has also been a problem to prevent the formation of powder clusters which interfere with the handling of the material.

It is the primary object of this invention to provide an apparatus which is capable of uniform application of the developing powder and which is simple in construction and operation.

It is a particular feature of the apparatus in accordance with the invention that in utilizing electromagnetic brushes in the form of cylinders, it provides control of the powder deposit and subsequent application thereof in accordance with the position of the sheet with respect to the brushes.

Other objects and features will be apparent from the following description of the invention, pointed out in particularity in the appended claims, and taken in connection with the accompanying drawings, in which:

FIG. 1 is a front elevational view in cross section of the developing powder applicator;

FIG. 2 is a rear view thereof;

FIG. 3 is a detail view showing the powder supply gate in open position;

FIG. 4 is a similar detail view showing the gate in closed position;

FIG. 5 is a perspective view of the apparatus partially in cross section; and

FIG. 6 is a view of a helical agitating rod.

Referring to the figures as seen in FIGS. 1, 2 and 5, the apparatus consists of an elongated casing 7, having a bottom portion 8, formed with a downwardly extending recess 9 and side cover portions 10 and 11. The front cover is not shown in FIGS. 1 and 5 in order to see the various working elements of the toner mechanism. In the back view shown in FIG. 2, the cover 13 is in place through which various shafts and gears extend, the operation of which will be referred to later.

The side covers 10 and 11 do not form a complete closure so that a rotating drum 15, which carries the electrostatically charged sheet 16, may be placed in close proximity to the powder applicator mechanism within the casing 7. The drum 15 is shown, by way of example, as a means for carrying the charged sheet 16 over the powder applicator assembly. It is generally a part of a reproducing or duplicating apparatus, which may include in addition an exposure unit and charging unit, with which the present invention is not concerned.

Various means may be utilized for holding the sheet 16 over the periphery over the drum 15. For example, a pair of belts as indicated by reference characters 17 and 13.

Within the casing 7, and journalled in the front and back covers thereof, are placed two cylinders 20 and 21 of non-magnetic material, such as brass or aluminum, the surface of each is studded with small magnetic cores 22, distributed over the entire area of the cylinder and closely spaced so that each forms individual magnets which attract the ferromagnetic powder 23 and form radially extending bristles 19. The bottom of casing 7 is filled with finely divided ferromagnetic material, such as iron powder 23, which is intermixed with suitable toner substance, as is well known in the electrophotographic art. The powder 23 is continuously agitated by a pair of agitator rods 24 and 24' which have a helical configuration and are located in the recessed portion 9. The agitator rods are inetrcoupled by intermeshing gears 25 and 25 as seen in FIG. 2. The gear 25 also meshes with gear 26 afiixed to the shaft 27 of the cylinder 21 and the gear 25', meshes with the gear 26' of the shaft 27 of the cylinder 20. In this manner, a complete drive assembly is obtained for the rotating elements within the casing 7. This assembly may be driven by a motor 38 coupled to the pinion 31 on the shaft 27. As seen by the intercoupling of the rotating elements, the cylinders 20 and 21, as well as the helical agitator rods 24 and 24, rotate in opposite directions. The ferromagnetic substance 23 is picked up by the closely spaced magnetic cores 22 and dense bristles 19 are formed over the surface of cylinders 20 and 21.

In accordance with the invention, means are provided for controlling the effective powder deposit on the rotating cylinders 20 and 21; namely, the application of this powder to the traveling sheet 16. It has been observed that a more uniform distribution of the powders is obtained on the surface of the copy material if the first application is in the direction of the travel of the sheet 16 and the second application in the opposite direction. This is related to a given size of the copy material; for example, a letter-size reproduction and the effective powder deposit on the surface of the cylinders 20 and 21 is controlled by the extent of travel of a given size of the copy material over the drum 15.

As seen in the detail views in FIGS. 3 and 4, a rotary gate 32 and 32 is provided for the cylinders 20 and 21, respectively. The gates 32 and 32 are in the form of an undercut shaft placed parallel to the cylinder surface. In one position, the undercut, or flat side 33 or 33, is facing the cylinder and thus allows free passage of the bristles 19, whereas in the other position, as seen in FIGS. 1 and 4, the gate 32 is turned so that the edge 34' nearly contacts the cylinder surface and thus scrapes off the powder bristles 19. The control of the respective rotation of the gates 32 and 32' may be effected in any desired manner. By way of example, a solenoid 37 is shown in FIG. 2 pivotally supported on the side of the casing 38. The shaft 39 of the solenoid 37 is interconnected with lever arm 40 and cranks 41 and 42 of the gates 32 and 32, respectively. A pair of closely spaced fixed scrapers 35 provided in the bottom of the casing to remove residual magnetic material from the surface of the cylinders.

The energizing of the solenoid 37 may be effected from any conventional circuit, not shown here, which iscontrolled by microswitches 44 and 45 schematically shown in FIG. 1, so placed that the leading edge of the copy material 16 will actuate these switches and hold them in actuated position as long as there is a copy sheet on the surface of the drum at the point between tangency of the drum with the cylinders 20 and 21. The gates operate in tandem so that when solenoid 37 is actuated, the gate 32 is closed and the gate 32' is open and vice versa.

In the operation, the motor 30 is energized by a switch mechanism, not shown, prior to the insertion of the copy material. The rotating assembly sets in motion the cylinders 20 and 21, as well as the agitators 24 and 24'. This solenoid is in such a position that the gate 32 is opened and 32' is closed. The sheet 16 entering the toner unit actuates the microswitch 44, which in turn, energizes the solenoid 37, closing the gate 32 and opening the gate 32'. As the sheet 16 is passed between the microswitches 44 and 45, the amount of developing powder material in the form of bristles accumulated over the roller 20 prior to the closing of the gate 32, is thus applied to the surface of the sheet 16. When the leading edge 46 of the sheet 16 closes the microswitch 45, the solenoid 37 is actuated again closing the gate 32 and thus the powder accumulated over the surface of the cylinder 21 is applied over the surface of the traveling sheet 16. The trailing edge 47 of the sheet 16 opens the microswitch 45 reestablishing the condition existing at the start of the operation. It is also practical to utilize the microswitch 45 to shut olf the motor 30, so that the entire apparatus is at a standstill until a sheet of paper is inserted under the drum to start the operation.

In the above manner, developing powder is applied to the surface of a charged sheet material from a magnetic brush which rotates in the direction of the travel of the paper for a certain period of time and then, from another brush rotating in the opposite direction of the travel of the paper. Both of these applications deposit a controlled amount, inasmuch as the amount of powder depositon each cylinder is determined in alternate sequence in accordance with the extent of travel of the charged sheet overthe magnetic brushes.

What is claimed is:

1. In an apparatus for applying a ferromagnetic powder for developing of a latent image on an electrostatically charged sheet, an elongated casing having a bottom portion adapted to hold finely divided ferromagnetic material, means for continuously agitating said material, a pair of adjacently placed cylinders in said casing having distributed on the surface thereon spaced magnetic cores adapted to attract discrete amounts of said powder and thereby forming bristles thereof extending radially from the surface of said cylinders, a rotating drum having means for supporting said charged sheet on the outer periphery thereof, said drum being arranged tangential to both said cylinders and in close proximity thereof for said bristles to contact the surface of said sheet, means for simultaneously rotating one of said cylinders in the direction of travel of said sheet and the other of said cylinders in the opposite direction thereto, and means associated with each of said cylinders for removing the powder deposit from said cylinders in alternate sequence in accordance with the extent of travel of said sheet over said cylinders.

2. Apparatus in accordance with claim 1 wherein said means for continuously agitating said material comprises a pair of shafts having laterally extending helical convolutions journaled in said housing and geared for'simultaneous rotation in opposite directions.

3. In an apparatus for applying a ferromagnetic powder for developing of a latent image on an electrostatically charged sheet, an elongated casing having a bottom portion adapted to hold finely divided ferromagnetic material, means for continuously agitating said material, a pair of adjacently placed cylinders in said casing having distributed on the surface thereon spaced magnetic cores adapted to attract discrete amounts of said powder and thereby forming bristles thereof extending radially from the surface of said cylinders, a rotating drum having means for supporting said charged sheet on the outer periphery thereof, said drum being arranged tangential to both said cylinders and in close proximity thereof for said bristles to contact the surface of said sheet, means for simultaneouly rotating one of said cylinders in the direction of travel of said sheet and the other of said cylinders in the opposite direction thereto, gate means associated with each of said cylinders for removing upon closure the powder deposit from the active surface thereof and means for closing one of said gates and simultaneously opening the other of said gates in alternate sequence during passage of said sheet over said cylinders.

4. In an apparatus for applying a ferromagnetic powder for developing of a latent image on an electrostatically charged sheet, an elongated casing having a bottom portion adapted to hold finely divided ferromagnetic material, means for continuously agitating said material, a pair of adjacently placed cylinders in said casing having distributed on the surface thereon spaced magnetic cores adapted to attract discrete amounts of said powder and thereby forming bristles thereof extending radially fromthe surface of said cylinders, a rotating drum having means for supporting said charged sheet on the outer periphery thereof, said drum being arranged tangential to both said cylinders and in close proximity thereof for said bristles to contact the surface of said sheet, means for rotating one of said cylinders in the direction of travel of said sheet and simultaneously rotating the other of said cylinders in the opposite direction, a pair of rotatable gate means each associated with one of said cylinders and each having a scraping edge adapted to engage the periphery of the associated cylinder for removing the powder adhering to the surface thereof, means for simultaneously rotating said gate meansin accordance with the extent of travel of said sheet over saidcylinders, the scrap ing edges of said pair of gate means being displaced for alternate engagement with the associated cylinder surface.

5. In an apparatus for applying a ferromagnetic powder for developing of a latent image on an electrostatically charged sheet, an elongated casing having a bottom portion adapted to hold finely divided ferromagnetic mate- 'rial, means for continuously agitating said material, a

pair of adjacently placed cylinders having distributed on the surface thereon spaced magnetic cores adapted to attract discrete amounts of said powder and thereby forming bristles thereof extending radially from the surface of said cylinders, a rotating drum having means for supporting said charged sheet on the outer periphery thereof, said drum being arranged tangential to both said cylinders and in close proximity thereof for said bristles to contact the surface of said sheet, means for rotating one of said cylinders in the direction of travel of said sheet and simultaneously rotating the otherof said cylinders in theopposite direction, a pair of rotatable gate means each associated with one of said cylinders and each having a scraping edge adapted to engage the periphery of the associated cylinder for removing the powder adhering to the surface thereof, means for simultaneously rotating said gate means in accordance with the extent of travel of said sheet over said cylinders, the scraping edges of said pair of gate means being displaced for alternate engagement with the associated cylinder surface, and control means actuated by the leading edge of said sheet for initiating the actuation of said rotating means.

6. Apparatus for applying toner powder to a sheet of paper as recited in claim 5 wherein said control means comprises spaced Inicroswitches positioned within the casing in the path of movement of said paper.

References Cited in the file of this patent UNITED STATES PATENTS Hayford et al Dec. 24, 1957 6 Grant Mar. 11, 1958 Reuter Sept. 16, 1958 Streich Oct. 10, 1961 

1. IN AN APPARATUS FOR APPLYING A FERROMAGNETIC POWDER FOR DEVELOPING OF A LATENT IMAGE ON AN ELECTROSTATICALLY CHARGED SHEET, AN ELONGATED CASING HAVING A BOTTOM PORTION ADPATED TO HOLD FINELY DIVIDED FERROMAGNETIC MATERIAL, MEANS FOR CONTINOUSLY AGITATING SAID MATERIAL, A PIAR OF ADJACENTLY PLACED CYLINDERS IN SAID CASING HAVING DISTRIBUTED ON THE SURFACE THEREON SPACED MAGNETIC CORES ADAPTED TO ATTRACT DISCRETE AMOUNTS OF SAID POWDER AND HEREBY FORMING BRISTLES THEREOF EXTENDING RADIALLY FROM THE SURFACE OF SAID CYLINDERS, A ROTATING DRUM HAVING MEANS FOR SUPPORTING SAID CHARGED SHEET ON THE OUTER PERIPHERY THEREOF, SAID DRUM BEING ARRANGED TANGENTIAL TO BOTH SAID CYLINDERS AND IN CLOSE PROXIMITY THEREOF FOR SAID BRISTLES TO CONTACT THE SURFACE OF SAID SHEET, MEANS FOR SIMULTANEOUSLY ROTATING ONE OF SAID CYLINDRES IN THE DIRECTION OF TRAVEL OF SAID SHEET AND OTHER OF SAID CYLINDRES IN THE OPPOSITE DIRECTION THERETO, AND MEANS ASSOCIATED WITH EACH OF SAID CYLINDERS FOR REMOVING THE POWDER DEPOSIT FROM SAID CYLINDERS IN ALTERNATE SEQUENCE IN ACCORDANCE WITH THE EXTENT OF TRAVEL OF SAID SHEET OVER SAID CYLINDERS. 